1. Field of the Invention
This invention relates to the field of polymer blends of the type suitable for the preparation of hot melt adhesives, coatings, sealants, as cable floods, for modifying asphalt or bitumens and as additives for plastics. More specifically, the invention relates to blended polymer compositions comprising (a) a copolymer of ethylene and an alphaolefin and (b) an amorphous polypropylene, or amorphous polyalphaolefin, or mixtures thereof.
2. Background of the Invention
Conventional amorphous polypropylenes, also known as "atactic polypropylenes" or "APP" are polymers which have been known and used for many years. They are tacky solid (at room temperatures), low molecular weight polymers having a low to very low level of crystallinity. Atactic polypropylenes originally were produced as undesired byproducts of the commercial production of isotactic polypropylene via the hydrocarbon solution or slurry processes, utilizing earlier versions of stereospecific catalysts. Although not the target products of those processes, APP nevertheless found commercial markets in such fields as adhesives, coatings, sealants, plastics, and asphalt or bitumen modifiers.
In recent years, commercial processes for the production of isotactic polypropylene have undergone improvement through advances in process technology and the availability of improved catalysts. The result has been improved selectivity of the processes and, concomitantly, reduced or eliminated production of the APP byproduct. At the same time, demand for an equivalent APP product has been rising as a result of increased commercial applications of the product. The result has been the development of various technologies for the intentional production of APP as a primary product. Intentional production technologies make possible tailored characteristics of the APP product to confer various properties. Intentionally produced versions of APP now is available as a homopolymer, copolymer or terpolymer and in a variety of molecular weight ranges. The terms "amorphous polyolefins" and "amorphous polyalphaolefins" often are used interchangeably to describe this new class of intentionally produced amorphous polypropylenes (homo-, co- and terpolymers). Since the method of production does not affect the nature or utility of the APP or APO product, as used herein, "amorphous polypropylene" and "APP" shall include both the byproduct and intentionally produced amorphous polypropylenes, while "amorphous polyolefin" and "APO" shall refer to amorphous polyolefins generally, including, amorphous polypropylene, as well as homo-, co- and terpolymers of amorphous polyolefins, regardless of whether produced as byproducts or by intent.
Polymer modifications of amorphous polypropylene, however produced, with various modifiers such as isotactic polypropylene, ethylene-propylene copolymer, polybutylene and low-density polyethylene, solely or in combination with other additives, are known in the prior art and have been utilized in the preparation of various compositions of commercial interest. See, for example, prior art U.S. Pat. Nos. 4,143,858; 3,900,694; 3,798,118; 4,826,909; and 4,761,450. However, the prior art has not suggested similar modification of amorphous polypropylenes or amorphous polyolefins with ethylene-alphaolefin copolymers of the type described herein.